In general, air conditioning circuits need to comply with a certain number of strict requirements regarding the ambient conditions in which the refrigerant, such as the fluid known by the designation R134A, circulates.
This is because it is necessary to avoid too many foreign bodies or foreign bodies of excessive size being present in the circuit as these can generate problems that can go so far as to break certain components of the air conditioning circuits, such as the compressor.
Furthermore, the refrigerant needs to be able to circulate in a moisture-free environment, because water molecules have a tendency to produce acid compounds in the presence of R134A and oil. Such compounds then attack the components of the circuit, and this may give rise to leaks and loss of functionality.
It is known practice to equip air conditioning circuits with cylinders containing a certain quantity of refrigerant in the liquid phase. These cylinders act, firstly, as fluid reservoirs intended to compensate for any potential leaks in the circuits and, secondly, to guarantee that, on leaving the cylinders, the refrigerant is completely in the liquid phase before it is transported further downstream. In particular embodiments, the outlet on the cylinder is led into a section of the condenser to make the liquid refrigerant undergo an additional pass, referred to as supercooling.
It is also known practice to benefit from the presence of reservoir cylinders in the path followed by the refrigerant to solve the environment problems mentioned hereinabove. To do that, a filter and a desiccant are placed inside the cylinders in order to eliminate as far as possible the presence of foreign bodies and moisture in the refrigerant circulation loops.
There are two broad categories of cylinder, namely cylinders referred to as added-on cylinders and cylinders referred to as inbuilt cylinders.
Added-on cylinders come already fitted with a filter and a desiccant. They are assembled with the condenser as a finishing operation, using screws and O-ring seals. However, while this type of cylinder has the advantage of being removable, it nonetheless demands a costly dedicated assembly operation.
Inbuilt cylinders are ready-assembled with the condenser and undergo the brazing process used for assembling the condenser.
If desiccant is present in the cylinder at the time of brazing, the desiccant will undergo a degassing which poses problems. Thus, an opening is provided on inbuilt cylinders through which opening the filter and the desiccant can be inserted inside the cylinders as a finishing operation, the opening being closed by a removable plug. It is also possible with this solution to change the filter and the desiccant at will without having to change the entire condenser.
In order to reduce manufacturing costs and the risks of leaks which are inherent in the sealing system using O-ring seals and removable plugs, there are advantages to be had in using sealed inbuilt cylinder systems.
Such sealed inbuilt cylinder systems are known, in which the opening for introducing the filter and the desiccant is closed by a cap which is sealed by tungsten inert gas (TIG) welding or by laser welding.
However, this solution is not very attractive in terms of cost, because TIG or laser welding as a finishing operation is relatively involved.
This is why cylinders prefitted with a filter and a desiccant, which are sealed and brazed in a single operation with the condenser when the latter is being brazed have been considered. This solution can prove to be highly economical because there are not other additional operations to be carried out on the condenser once it has left the brazing furnace.
However, one difficulty with this type of solution still remains and lies in the way in which the desiccant behaves during the brazing process. More specifically, at high temperature, this desiccant has a tendency to diffuse, toward the condenser with which it communicates, moisture which contaminates the neutral atmosphere of the furnace and disrupts the brazing operation. This results in leaks in the manufactured condensers and means that this solution cannot be industrialized.